The invention relates to a method for control of an automatic transmission driven by an internal combustion engine wherein an electronic gear control tests whether a cold start condition exists.
In electrohydraulic automatic transmissions, a so-called warm-up program or warm-up shift characteristic field is usually integrated in the software of the electronic gear control. When the warm-up program is activated, the shift points of the automatic transmission are moved to higher rotational speed values of the internal combustion engine or of the transmission output rotational speed. Hereby is obtained that the internal combustion engine and the catalyst warm up quicker and thus more quickly reach the ideal operating temperature. Thus, DE-OS 39 28 814, e.g. proposes that a cold start condition of the motor vehicle is detected by means of a temperature sensor, and that for a limited period of time the electronic gear control, via a warm-up shift program, shifts the gear steps of the automatic transmission. It is also proposed that the temperature detected by the sensor is the coolant temperature of the internal combustion engine or the temperature of the ATF (automatic transmission fluid).
The time step, mentioned in the above described prior art, is usually determined by the passenger car manufacturers by means of exhaust gas test on a roller test bench. The problem resulting from this is that the actual road operation differs from the exhaust gas. For example, if the vehicle is already stopped after a short time and again started, the time step again begins to run in all its length.
The problem, which the invention is based, consists in developing a warm-up program oriented to the actual driving operation.
According to the invention, a first solution of the problem consists in that the electronic gear control, when the cold start condition exists, determines from the torque generated by the internal combustion engine and the rotational speed thereof, the power generated by the internal combustion engine. From two power values calculated within one time period, the energy throughput is determined and added to the former energy throughput. With the added energy throughput is then associated, via a characteristic line, a first driving activity wherein the first driving activity causes higher shift points of the automatic transmission. Thereafter, the electronic gear control compares the first driving activity with the second driving activity, the second driving activity being determined from the actual behavior of the driver. The second driving activity can be determined, e.g. by means of a method such as disclosed in German Patent 39 22 051. The first inventive solution is thus preferably applicable to automatic transmissions which have available a so-called "intelligent shift program" i.e. a shift point is selected in accordance with the driver's behavior.
In a development of this, it is proposed that the first driving activity determines the shift points of the automatic transmission when the activity is greater than the second driving activity. In one other development, it is proposed that the second driving activity determines the shift points when the first driving activity is lesser than or equal to the second driving activity.
The inventive solution and the developments thereof offer the advantage that the actual state of the internal combustion engine, i.e. the temperature can be clearly determined by its energy throughput. By the summing up and the first driving activity resulting therefrom, it is brought about that the shift points be moved to higher values. The coordination by means of characteristic line is here carried out in a manner such that a higher sum of the energy throughput produces a lower first driving activity. By the two developments, i.e. according to the comparison of the first with the second driving activity, the warm-up program is activated or de-activated.
According to the invention, the second solution of the problem consists of the electronic gear control determines the energy throughput calculated from the generated power of the internal combustion engine and adds it to the former energy throughput. Thereafter, the summed up energy throughput is compared with a limit value and the shift program preset by a driver is activated when the summed up energy throughput is higher than the limit value. This solution is thus preferably applicable to automatic transmissions where a driver can manually select a shift program such as economy, sport or winter.